docs: def convert(self, imtls, nsites, idx=0):
          """
          Convert a probability map into a composite array of length `nsites`
          and dtype `imtls.dt`.
  
          :param imtls:
              DictArray instance
          :param nsites:
              the total number of sites
          :param idx:
              index on the z-axis (default 0)
          """
          curves = numpy.zeros(nsites, imtls.dt)
          for imt in curves.dtype.names:
              curves_by_imt = curves[imt]
              for sid in self:
                  curves_by_imt[sid] = self[sid].array[imtls(imt), idx]
          return curves